<!DOCTYPE html>
<html class="reftest-wait">
<title>Update callback should only be called once</title>
<link rel="author" title="Tim Nguyen" href="https://github.com/nt1m">
<link rel="help" href="https://drafts.csswg.org/css-view-transitions-1/#call-dom-update-callback-algorithm">
<link rel="match" href="../../../../expected/wpt-import/css/reference/ref-filled-green-100px-square.xht">
<meta name="fuzzy" content="maxDifference=0-1; totalPixels=0-500">
<style>
    #target {
        width: 100px;
        height: 100px;
        background-color: red;
    }

    ::view-transition-group(*),
    ::view-transition-image-pair(*),
    ::view-transition-old(*),
    ::view-transition-new(*) {
      animation-play-state: paused;
    }
</style>
<p>Test passes if there is a filled green square and <strong>no red</strong>.</p>
<div id="target"></div>
<script>
    addEventListener("load", () => {
        let updateCallbackCalled = false;
        document.startViewTransition(function() {
            target.style.backgroundColor = updateCallbackCalled ? "red" : "green";
            updateCallbackCalled = true;
            document.startViewTransition(() => {});
            requestAnimationFrame(() => {
                requestAnimationFrame(() => {
                    document.documentElement.classList.remove("reftest-wait");
                });
            });
        });
    });
</script>
</html>
